MEXICO CITY, Oct 18 (Reuters) - Mexican state oil company Pemex approved a joint venture for two shallow water fields in the Gulf of Mexico, the firm said on Tuesday, marking the second time the company will seek partners to boost declining crude oil output.

The joint venture will cover Pemex’s Ayin and Batsil fields off the coast of Campeche state, which contain 46 million barrels of oil equivalent (boe) in proven reserves.

The company added that the two fields contain estimated proven, probable and possible (3P) recourses of some 281 million boe.

A sweeping energy overhaul finalized in 2014, which ended Pemex’s monopoly over exploration and production of oil and gas also permitted the company to enter into joint ventures in a bid to reverse a slump in crude output.

“(Pemex) is promoting the formation of alliances as a strategic route to improve its operations and generate profits for the benefit of the country,” the company said in a statement.

Falling from a 2004 peak of 3.38 million barrels per day (bpd) of crude production, output stands at about 2.19 million bpd so far this year.

Pemex’s partner in the shallow water joint venture could be announced in March 2017, the company said, at the same time that 15 other fields will be up for grabs in the first installment of a second set of rolling oil auctions.

The company will aim to increase production by 70,000 bpd before the end of 2020, and the development of the Ayin and Batsil fields will require an investment of some $4.2 billion in infrastructure, Director General of Exploration and Production at Pemex, Javier Hinojosa, said Tuesday night in a radio interview.

The executive added Pemex will use so-called farm outs for exploration and production of the onshore fields of Ogarrio, Mora and Cardenas, which have already been approved by the company’s board and included in the bidding round 2.2.

The company’s first joint venture covers its Trion deep water block in the Perdido Fold Belt near Mexico’s maritime border with the United States.

Its partner on the potentially lucrative Trion field is scheduled to be announced on December 5. (Reporting by Adriana Barrea and David Alire Garcia; Editing by Andrew Hay and Vyas Mohan)